Red Drum \u3ci\u3e(Sciaenops ocellatus)\u3c/i\u3e Trophic Web Reconstruction Using Stable Isotopes in Two Systems in the Northwestern Gulf of Mexico

Estuaries act as nurseries for many important fishes, including predators like Red Drum (Sciaenops ocellatus). Using gut content and stable isotope analyses to better understand juvenile S. ocellatus’ diet and role within the trophic web, a full year of data was collected on a quarterly basis to illustrate a change in diet based on resource availability at two study sites and for two non-overlapping S. ocellatus sizes. Panopeidae and Penaeidae were the most abundant prey items found in S. ocellatus stomachs for both sizes, sites, and four quarters representing over 50% of the diet. Stable isotope analyses from 80 fish show that S. ocellatus are feeding in very similar trophic levels but nonetheless there are significant differences for all quarters in δ15N between sites and δ13C between sizes, sites, and quarters. Differences may be linked to changing resources throughout the year, site composition differences, and seasonal changes in productivity

Current status of dairy cow feeding in the Ethiopian Central Highlands and some recommendations for promising technologies

This leaflet is an extract from a study commissioned by SNV Support to Business Organisation and the Access to Markets Program (BOAM) in its Milk and Milk Products Value Chain Sub-program. The study focused on the client farmers’ and members of dairy farmer cooperatives’ state of knowledge and practice of feeding dairy animals in Jimma, Addis Alem, Debre Markos, Sululta and Selale. The leaflet highlights the major on the current status of feeding practices for dairy animals and some recommendations which can be used for most of the Central Highlands of Ethiopia

Canada-US Softwood Lumber Trade Revisited: Examining the Role of Substitution Bias in the Context of a Spatial Price Equilibrium Framework

In the last two decades, softwood lumber trade between Canada and the United States has been characterized by numerous trade restrictions. Many studies have attempted to quantify the effects of such sanctions, and in doing so, softwood lumber was modeled as a single, homogenous commodity. However, recent research has suggested that this may be a misleading assumption, since not all softwood lumber products are equivalent substitutes. We refer to this problem as the substitution bias, and uniquely address this issue in estimating the effects of trade restricting policies. Using a spatial price equilibrium (spe) model, impacts of the post-sla import duties are estimated and compared to estimates of two alternative policy regimes – an export tax and quota. By controlling for substitution bias, our estimates indicate a larger share of the tariff burden is placed on us consumers, with Canadian producers suffering less injury compared to estimates using the traditional homogenous lumber assumption. In addition, by comparing the net impact associated with the alternative policy regimes, a policy equivalence result is found. Our results suggest that the short-run impact of a trade restriction is largely independent of the policy regime incorporated, with the collection of quota rents or tax revenues determining overall winners and losers.Softwood lumber trade, spatial price equilibrium, lumber substitutability

A Generally Covariant Theory of Quantized Dirac Field in de Sitter Spacetime

As a sequel to our previous work\cite{Feng2020}, we propose in this paper a quantization scheme for Dirac field in de Sitter spacetime. Our scheme is covariant under both general transformations and Lorentz transformations. We first present a Hamiltonian structure, then quantize the field following the standard approach of constrained systems. For the free field, the time-dependent quantized Hamiltonian is diagonalized by Bogliubov transformation and the eigen-states at each instant are interpreted as the observed particle states at that instant. The measurable energy-momentum of observed particle/antiparticles are the same as obtained for Klein-Gordon field. Moreover, the energy-momentum also satisfies geodesic equation, a feature justifying its measurability. As in \cite{Feng2020}, though the mathematics is carried out in terms of conformal coordinates for the sake of convenience, the whole theory can be transformed into any other coordinates based on general covariance. It is concluded that particle/antiparticle states, such as vacuum states in particular are time-dependent and vacuum states at one time evolves into non-vacuum states at later times. Formalism of perturbational calculation is provided with an extended Dirac picture.Comment: 15 pages. arXiv admin note: text overlap with arXiv:2003.0989